US8577434B2 - Coaxial LED light sources - Google Patents

Abstract

An emitter device may include at least two emitters, such as LEDs. The coaxially disposed emitters may emit light in substantially the same area so that no apparent distance is perceived between individual emitters, as in emitter devices in which the emitters are disposed adjacent one another. The coaxially disposed emitters may include emitters suitable for pulse oximetry and/or water fraction measurements, for example.

Description

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/009,277, filed Dec. 27, 2007, and is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates generally to medical monitoring devices and, more particularly, to sensors used for medical monitoring devices.

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring physiological characteristics of a patient. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine.

One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient.

Pulse oximeters typically utilize a non-invasive sensor that transmits light through a patient's tissue and that photoelectrically senses the absorption and/or scattering of the transmitted light in such tissue. One or more of the above physiological characteristics may then be calculated based upon the amount of light absorbed or scattered. More specifically, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed or scattered by the blood in an amount correlative to the amount of the blood constituent present in the blood. The amount of light absorbed and/or scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms.

Light emitting diodes (LEDs) are commonly used as the light source for pulse oximeters. When more than one wavelength of light is needed, as is often the case, multiple LEDs are present in the device. The variances in the respective locations of the LEDs can affect the pathlengths of the emitted light and may be calibrated out of the resulting measurements. This would typically require additional hardware and software to implement. Furthermore, when these light sources are contained in a disposable sensor, the presence of these light sources increase the cost of replacement sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 illustrates an exemplary pulse oximeter and sensor.

FIG. 2 illustrates an exemplary pulse oximeter system which features a coaxial LED unit in the pulse oximeter, in accordance with an embodiment of the present disclosure.

FIG. 3 illustrates an exemplary pulse oximeter system which has a sensor that features a coaxial LED unit in accordance with an embodiment of the present disclosure.

FIGS. 4A and B illustrate a coaxial LED unit in accordance with an embodiment of the present disclosure.

FIGS. 5A and B illustrate a coaxial LED unit in accordance with another embodiment of the present disclosure.

FIGS. 6A-C illustrate different views of a coaxial LED unit in accordance with an alternate embodiment of the present disclosure.

FIGS. 7A-C illustrate coaxial LED units containing four LEDs, made in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

As discussed previously, many medical monitoring devices use multiple light sources to monitor a patient's physiological state. The pathlengths of the light emitted and used to monitor physiological characteristics are important for accurate measurement; any factors which may affect the expected pathlength of the emitted light should be accounted for. This is may be accomplished by calibrating the data received by the monitoring device.

InFIG. 1, an exemplary medical monitor is shown that comprises apulse oximeter monitor10 that is coupled by acable12 to a sensor, illustrated generically as asensor14. Thesensor14 may be coupled to a transmission device (not shown), instead of thepulse oximeter monitor10, to facilitate wireless transmission between thesensor14 and thepulse oximeter monitor10. The pulse oximeter may be any suitable pulse oximeter, such as those available from Nellcor Puritan Bennett LLC. Thesensor14 aids in illuminating an object, such as a human finger or earlobe, and transmits the information back to thepulse oximeter10 via thecable12. The sensor may include an encoding device, such as a resistor and/or a memory, to provide the monitor with information that it may use for calibration and/or other operational purposes.

As shown inFIGS. 2 and 3, thesensor14 includes anemitter22 and adetector24 that may be of any suitable type. For example, theemitter22 may be one or more LEDs adapted to transmit one or more wavelengths of light in the red to infrared range, and thedetector24 may be a photodetector selected to receive light in the range or ranges emitted from theemitter22. For pulse oximetry applications using either transmission or reflectance type sensors, the oxygen saturation of the patient's arterial blood may be determined using two or more wavelengths of light, most commonly red and near infrared wavelengths. Similarly, in other applications, a tissue water fraction (or other body fluid related metric) or a concentration of one or more biochemical components in an aqueous environment may be measured using two or more wavelengths of light, most commonly near infrared wavelengths between about 1,000 nm to about 2,500 nm. It should be understood that, as used herein, the term “light” may refer to one or more of infrared, visible, ultraviolet, or even X-ray electromagnetic radiation, and may also include any wavelength within the infrared, visible, ultraviolet, or X-ray spectra.

In the case of pulse oximeters, these devices use two different wavelengths to measure different blood flow characteristics, and two LEDs are commonly used as light sources. These LEDs can be located in the pulse oximeter monitor itself or in the sensor. If the LEDs are located in the pulse oximeter monitor, each LED may be coupled to an optical fiber which conveys the emitted light to the object being illuminated. If the LEDs are located in the sensor, the LEDs may be coupled to a controller which controls the function of the LEDs.

Currently, the LEDs used in a pulse oximeter sensor may be 10 to 12 thousandths of an inch wide and located next to each other on separate metal pads, about one to two millimeters apart. Thus, they will emit light of slightly different pathlengths. As measurements taken with different wavelengths of light are best taken when the different wavelengths are emitted from the same location, this one to two millimeter separation between the LEDs can affect the accuracy of the measurements. The separation may be calibrated out, but this typically requires additional software and/or hardware. Another method of working around the distortions caused by the separation between then LEDs is to use a complex beam combining system, which typically results in higher costs and loss of light. What is needed is a solution which simplifies the use of multiple light sources.

A coaxial LED, in accordance with one embodiment, eliminates the need to calibrate out the separation distance between multiple LEDs and also reduces or eliminates additional hardware and/or software. By using a coaxial LED in the pulse oximeter monitor, only one optical fiber may be used to transmit red and infrared photons, instead of the two optical fibers currently needed—one each for the red and infrared LEDs. This would make the sensors easier to replace as the sensors would have fewer parts to be connected as only one optical fiber is needed to connect the coaxial LED to the monitor.

For example, inFIG. 2, theemitter22 and thedetector24 are located inside thepulse oximeter monitor10. The pulse oximeter monitor10 also contains acontroller16 which monitors and dictates the function of thecoaxial LED18 of theemitter22, as well as the rest of the system. Theemitter22 is coupled to anemitter window23 in thesensor14 through one or moreoptical fibers20 located in thecable12. Theemitter22 transmits light to theemitter window23 to illuminate the target object and adetector24 receives the reflected light and sends the information back through thecable12 to thecontroller16.

Thesensor14 may be made of any suitable material, such as plastic, foam, woven material, or paper. Thecable12 may be permanently coupled to thesensor14, or it may be removably coupled to thesensor14—the latter alternative being more useful and cost efficient in situations where thesensor14 is disposable.

In an alternate configuration, as shown inFIG. 3, thecoaxial LED18 is located inside theemitter22 in thesensor14. Thecoaxial LED18 is coupled to thecontroller16 in thepulse oximeter10 by a wire26 in thecable12. Theemitter22 illuminates the target object, and adetector24 in thesensor14 receives the reflected light and sends the information back through thecable12 to thecontroller16.

According to one embodiment, to create acoaxial LED unit18, the LEDs may be formed separately and then combined into one unit, with at least one of the LEDs being relatively transparent to the other LED. For example, a first LED may be made by growing an epilayer on a GaAs substrate and doping it to create the PN junction of the LED. The GaAs substrate can then be removed to leave only the transparent epilayer as the LED. If the first LED is a red LED, this epilayer is transparent to infrared waves/photons. The first LED may be coupled to a ring contact or annular substrate. A second LED may be formed in a similar manner. The second LED, which may be transparent or opaque, may be mounted on a substrate and then mounted directly below the first LED to create acoaxial LED unit18. Thecoaxial unit18 can be encapsulated in its entirety in a material with a refractive index that maximizes the optical efficiency of the unit.

One example of acoaxial LED unit18, made in accordance with the method described above, is shown inFIGS. 4A and B. In both figures, a cross-section of an exemplarycoaxial LED unit18 is shown. Afirst LED28 is coupled to an annular substrate orring contact34. Thefirst LED28 and thering contact34 are created above asecond LED30, which may be disposed on asubstrate32. There may be an insulatingmaterial36 between thering contact34 and thesubstrate32. The insulatingmaterial36 may be a dielectric material. As shown inFIG. 4A, when thefirst LED28 is turned on, the portion of thefirst LED28 that is in contact with thering contact34 emitslight38. Similarly, when thesecond LED30 is turned on, via a contact in thesubstrate32, it emits light40. Because thefirst LED28 is transparent in relation to the light emitted by thesecond LED30, the emittedlight40 is transmitted through thefirst LED28. The emittedlight38 and40 may be incident to an object such as anoptical fiber20 or a patient's tissue.

In another embodiment, a second LED may be mounted on a substrate with a polished surface. The first LED is mounted directly above the second LED. Acoaxial LED unit18 made by this method is shown inFIGS. 5A and B. In both figures, a cross-section of an exemplary coaxial LED unit is shown. Afirst LED42 is coupled to a ring contact orannular substrate46. Thefirst LED42 and thering contact46 are mounted above asecond LED44, which is coupled to a ring contact/annular substrate47. Thering contact47 of thesecond LED44 also may be coupled to asubstrate50 having apolished surface51. As was shown inFIG. 4, insulatingmaterial48 may be placed between thering contacts46 and47. InFIG. 5A, when thefirst LED42 is turned on, it emits light52. However, given the nature of LEDs, light is emitted in all directions from thefirst LED42. Some of this light52 will strike the polished surfaces of thesubstrate50 and be reflected back as reflectedlight56. This helps to minimize changes in the wavelength of the light being emitted by the first LED as some of the light52 would normally be absorbed and re-emitted by thesubstrate50, which could affect the wavelength of the light being transmitted. InFIG. 5B, when thesecond LED44 is turned on, the portions of thesecond LED42 in contact with thering contact47 will emit light54. Some of the emitted light54 will strike thepolished surface51 of thesubstrate50 and be bounced back as reflectedlight56. The emittedlight52 and54 and the reflected light56 may be incident to an object such as anoptical fiber20 or a patient's tissue.

An alternative embodiment is shown inFIGS. 6A-C,FIG. 6A offers a top-side view of an exemplarycoaxial LED18, where afirst LED58 is surrounded by asecond LED60 in a ring-like fashion. Thisfirst LED58 is coupled to a contact pad orsubstrate62. Asecond LED60 is formed so that thesecond LED60 is in the shape of a disk with an empty space in the middle, the empty space in thesecond LED60 being sized to accommodate thefirst LED58. Thesecond LED60 is mounted on the same substrate as thefirst LED58, with thesecond LED60 surrounding thefirst LED58. Any gaps remaining between the twoLEDs58 and60 may be filled with an insulating material.FIGS. 6B and C offer cross-sectional views of the exemplarycoaxial LED unit18 ofFIG. 6A. In bothFIG. 6B andFIG. 6C, both thefirst LED58 and thesecond LED60 are coupled to asubstrate62. As shown inFIG. 6B, when thefirst LED58 is turned on, it emits light64, and as shown inFIG. 6C, when thesecond LED60 is turned on, it emits light66. The emittedlight62 and64 may be incident to an object such as anoptical fiber20 or a patient's tissue.

Each of the methods for creating a coaxial LED unit described above may be repeated to create coaxial LED units comprising more than two LEDs. For example,FIGS. 7A-C show coaxial LED units with four LED layers made using the methods above.FIG. 7A shows a coaxial LED unit made with the same method as the coaxial LED unit shown inFIGS. 4A and B. InFIG. 7A,LEDs70,72 and74 are coupled torespective ring contacts78, and mounted one beneath the other. The threeLEDs70,72 and74 andrespective ring contacts78 are disposed over anLED76. The stack of LEDs is then disposed on asubstrate82 to form acoaxial LED unit18. The spaces between thering contacts78 may be filled with an insulatingmaterial80.

FIG. 7B shows a coaxial LED unit made with the same method as the coaxial LED unit shown inFIGS. 5A and B. InFIG. 7B,LEDs84,86,88, and90 are coupled to ringcontacts94, and mounted one beneath the other. TheLEDs84,86,88, and90 andring contacts94 are mounted to apolished substrate96 to form acoaxial LED unit18. The spaces between thering contacts94 may be filled with an insulatingmaterial92.

FIG. 7C shows a coaxial LED unit made with the same method as the coaxial LED unit shown inFIGS. 6A-C. InFIG. 7C,LEDs100,102,104, and106 are mounted on a substrate (not shown) in such a manner than theLEDs100,102,104, and106 are nested within each other. Any gaps between theLEDS100,102,104, and106 may be filled with an insulating material (not shown). Each of thecoaxial LED units18 shown inFIGS. 7A-C can be encapsulated in its entirety in a material with a refractive index that maximizes the optical efficiency of the unit.

For the embodiments discussed above, it will be evident to those of ordinary skill in the art the appropriate electronic connections to be made to these coaxial LEDs. For simplification, those connections will not be discussed in detail here. It will also be evident that these LEDs are not constrained to only being formed in a circular manner but may be formed in other geometric formations as well.

These coaxial LEDs may be used in many applications other than pulse oximeters. It can be used by other medical monitoring devices such as an optical spectrophotometer to measure bodily fluid related metrics. This may require using three or more different wavelengths of light. The coaxial LED can be used as power or warning indicators in consumer electronics, optical analyzers, and other technologies where it would be useful to have a single light source that produces multiple frequencies. The coaxial LEDs may also emit more than just two wavelengths of light. It can be formed to utilize three or four LEDs for applications requiring multiple wavelengths, such as for applications measuring body fluid related metrics.

Claims (20)

What is claimed is:

1. An emitter assembly comprising:

a first LED coupled to a first substrate having an opening therein, the first LED being generally positioned across the opening; and

a second LED coupled to a second substrate and generally disposed to emit light into the opening and generally toward the first LED, the first LED being generally transparent to the light emitted from the second LED, wherein the opening is disposed between the first LED and the second LED.

2. The emitter assembly, as set forth inclaim 1, wherein the first LED generally emits red light and wherein the second LED generally emits infrared light.

3. The emitter assembly, as set forth inclaim 2, wherein the first and second LEDs are generally suitable for pulse oximetry measurements.

4. The emitter assembly, as set forth inclaim 1, wherein the first LED and the second LED emit light of different wavelengths, the wavelengths being generally suitable for water fraction measurements.

5. The emitter assembly as set forth inclaim 1, wherein the first substrate comprises a dielectric material generally configured to electrically insulate the first substrate from the second substrate.

6. The emitter assembly, as set forth inclaim 1, wherein the second substrate comprises a generally reflective surface positioned to reflect light emitted from the first and second LEDs generally into the opening and toward the first LED.

7. The emitter assembly, as set forth inclaim 6, wherein the first substrate comprises a first ring contact electrically coupled to the first LED and wherein the second substrate comprises a second ring contact electrically coupled to the second LED.

8. The emitter assembly, as set forth inclaim 1, wherein the first LED is configured to emit light from a first portion of the first LED that is in contact with the first substrate.

9. The emitter assembly, as set forth inclaim 1, wherein the emitter is encapsulated in a material with a refractive index configured to increase optical efficiency of the emitter assembly.

10. A sensor assembly comprising:

a housing;

an emitter disposed generally within the housing, the emitter comprising a first LED coupled to a first substrate comprising an opening therein, the first LED being generally positioned on a first side of the opening and across the opening, and the emitter further comprising a second LED coupled to a second substrate and generally disposed on a second side of the opening opposite the first side and configured to emit light into the opening and generally toward the first LED, the first LED being generally transparent to the light emitted from the second LED, the first and second LEDs being configured to emit light generally into a tissue site; and

a detector disposed generally within the housing and being configured to detect light from the first and second LEDs which has passed through the tissue site.

11. The sensor assembly, as set forth inclaim 10, wherein the first LED emits red light and wherein the second LED emits infrared light.

12. The sensor assembly, as set forth inclaim 11, where in the first and second LEDs are generally suitable for pulse oximetry measurements.

13. The sensor assembly, as set forth inclaim 10, wherein the first LED and the second LED emit light of different wavelengths, the wavelengths being generally suitable for water fraction measurements.

14. The sensor assembly, as set forth inclaim 10, wherein the first substrate comprises a dielectric material to generally electrically insulate the first substrate from the second substrate.

15. The sensor assembly, as set forth inclaim 10, wherein the second substrate comprises an electrical contact for the second LED.

16. The sensor assembly, as set forth inclaim 10, wherein the second substrate comprises a reflective surface generally positioned to reflect light emitted from the first and second LEDs into the opening and generally toward the first LED.

17. The sensor assembly, as set forth inclaim 16, wherein the first substrate comprises a first ring contact electrically coupled to the first LED and wherein the second substrate comprises a second ring contact electrically coupled to the second LED.

18. The sensor assembly, as set forth inclaim 10, comprising an encoding device configured to deliver information to a monitor associated with the sensor assembly.

19. The sensor assembly, as set forth inclaim 10, wherein the first LED is configured to emit light from a portion of the first LED that is in contact with the first substrate.

20. The sensor assembly, as set forth inclaim 10, wherein the sensor assembly is configured to communicate wirelessly with a monitor.

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